Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Goes well beyond the annotations: it states the write is to the ledger, discloses the per-call confirmation default and that it can be disabled, warns that the action 'reaches other people' requiring user confirmation, and names the required Cotlet API key scope. This is richer side-effect and auth context than readOnlyHint/destructiveHint alone convey.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Purpose is front-loaded, but the first two sentences restate the same thing ('Book a supplier invoice as a purchase entry with its lines' / 'Creates a purchase entry for a supplier with its lines, in one call'), which is redundant. The remaining operational sentences each earn their place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description helpfully notes it returns the entry number and total, and covers the write-to-ledger effect, confirmation requirement, auth scope, and the PDF boundary. Complete enough to call correctly, with only minor gaps (e.g. how lines/VAT codes are validated).

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents supplier, invoice_number, entry_date, lines, and division. The description adds no field-level syntax or format detail (e.g. how lines should be structured, division defaulting), so baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: 'Book a supplier invoice as a purchase entry with its lines' and 'Creates a purchase entry for a supplier.' This distinguishes it from the sales-invoice and journal-entry siblings implicitly (supplier invoice/purchase vs. sales), though it never names an alternative tool outright.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It clarifies a boundary ('Attaching the invoice PDF is not part of this tool') and notes the confirmation workflow, but gives no explicit when-to-use-some-other-tool guidance or prerequisite (e.g. use search_relations first). Usage is implied by the accountant context rather than stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.